In drilling operations, a hydraulic catwalk is often used to move pipe from a storage location to a desired position on the drilling rig and, when the pipe is being removed from the well, to move the pipe from the drilling rig to the storage location.
Examples of hydraulic catwalks are shown in U.S. Pat. Nos. 4,379,676, 4,347,028, 4,474,520, 7,163,367, and 8,052,368. When a pipe is being removed from a well it is moved into a raised position on the drilling rig, the free end of the pipe is laid on the ramp of the hydraulic catwalk and the pipe is released. The pipe is then removed from the bottom of the ramp and placed in a holding in a pipe rack or storage area. The pipe may obtain considerable momentum as it slides down the ramp and this can damage the pipe and components of the catwalk. On at least one system a shock absorber is employed to absorb some of the impact forces from the pipe hitting the end of the ramp.
It will be appreciated that such a shock absorber must withstand repeated impacts from pipes being lowered onto the ramp. For example, pipe is normally in 30 foot lengths, so a 9,000-foot well would require 300 such pipes. Removing all of these pipes from the well will therefore subject the shock absorber to 300 such impacts. It has been found, however, that shock absorbers used with some contemporary hydraulic catwalks do not withstand very well the repeated impacts from the pipe being lowered onto the ramp and then released. In fact, some commonly-used shock absorbers have been known to fail during the pipe retraction sequence for a single well. This slows the pipe removal process until the shock absorber has been replaced.